Porous Co9S8 Nanosheet Arrays@Co Foam Electrode via in Situ Sulfidation at Room Temperature for Superior Supercapacitors

In this work, novel porous Co 9 S 8 nanosheet arrays are prepared on Co foam through a simple and scalable chemical liquid-phase processing strategy, which involves the uniform growth of cobalt hydroxide hydrogen phosphate microbelts followed by subsequent in situ sulfidation with sodium sulfide at room temperature. As-prepared porous Co 9 S 8 nanosheet arrays can be directly used as binderless electrodes for a supercapacitor. Even at a high mass loading of 11.54 mg cm –2, it delivers a high capacitance of 14518.9 mF cm –2 (1279.4 F g –1 ) and an exceptional cycle life with a capacitance retention of 85.7% after 15000 cycles at 200 mA cm –2 . Moreover, an assembled asymmetric supercapacitor based on an activated carbon negative electrode delivers an encouraging energy density (42.9 W h kg –1 at 828.5 W kg –1 ) and an excellent cycle life (86% retention after 10000 cycles). This method can be extended to design and construct other high-performance sulfide electrodes for supercapacitors and other energy storage systems.